Picture coding device and picture decoding device

ABSTRACT

If coding is carried out on the block basis on subband coding of an image, the hierarchical characteristic which a subband image inherently has would be lost. Thus, efficient coding is to be carried out while holding the hierarchical characteristic of the subband image. After the subband image is coded on the block basis, symbol information and coefficient information are decomposed and relocated for every subband before producing coded data.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP98/00359 which has an Internationalfiling date of Jan. 29, 1998 which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a digital image processing technology,and in particular to an image coding device for coding image data with ahigh efficiency and an image decoding device for decoding the coded datawhich has been coded by the image coding device.

BACKGROUND ART

Recently, subband coding techniques have been proposed as highlyefficient image coding and decoding techniques. Among the subband codingtechniques, a technique for decomposing an image into bands as shown inFIG. 16 in which analysis of an input image is carried out by means of aband decomposing filter bank has been generally known as a techniquehaving a high coding efficiency. Such a technique is described by, forexample, Fujii and Nomura “Topics on Wavelet Transform”, technicalreport, IEICE, Institute of Electronics, Information and CommunicationEngineers, IE 92-11(1992).

FIG. 16 shows subband images which are obtained by conducting twodimensional subband decomposition for an input signal three times. Ahorizontal high frequency and vertical low frequency subband which isobtained by the first decomposition is designated as HL1. A horizontallow frequency and vertical high frequency subband is designated as LH1.A horizontal high frequency and vertical high frequency subband isdesignated as HH1. Subbands HL2, LH2 and HH2 are obtained as similarlyto the foregoing by conducting second two-dimensional subbanddecomposition for the horizontal low frequency and vertical lowfrequency subband.

Subband HL3, LH3 and HH3 are obtained similarly to the foregoing byconducting third two-dimensional subband decomposition for thehorizontal low frequency and vertical low frequency subband which hasbeen obtained by second decomposition. A horizontal low frequency andvertical low frequency subband at this time is designated as LL3. Thefilter bank which is used for decomposing band may use a filter bank forwavelet transformation and a subband decomposing synthesizing filterbank and the like. The image which has been decomposed into subbands insuch a manner has a hierarchical structure.

As a recent technique having the highest coding efficiency which iscapable of adapting to the subband images, a ZTE (Zero Tree Entropycoding) technique using the above-mentioned hierarchical structure hasbeen proposed (ISO/IEC JTC/SC29/WG11/MPEG95/N0441,ISO/IECJTC1/SC29/WG11/MPEG96/M0637, ISO/IEC JTC1/SC29/WG11/MPEG96/M1539).

Now, the ZTE technique will be described. In the ZTE technique, a blockstructure which is shown in FIG. 18 is formed by collecting subbandcoefficients (hereinafter referred to as coefficients) corresponding tothe same spacial positions which are linked with each other by arrows asshown in FIG. 17 from the image which has been decomposed in subbands.It has already known that there is a correlation between coefficientswhich are linked with each other by arrows in FIG. 17 excepting thehighest frequency subbands.

The whole relation of the coefficients which are linked with each otherby arrows in FIG. 17 is referred to as “trees”. One coefficient of eachof the subbands (LH3, HL3, HH3) having a frequency one level higher thanthat of one coefficient of the lowest frequency subband (LL3)corresponds thereto (for example, a1, a2 and a3 correspond to a0 in FIG.17). Four coefficients of each of the subbands (LH2, HL2, HH2) having afrequency one level higher than that of each of these coefficientscorrespond thereto (for example, a10, a11, a12, a13 correspond to a1 inFIG. 17). Sixteen coefficients of each of the subbands (LH1, HL1, HH1)having a frequency one level higher than that of each of fourcoefficients correspond thereto. Trees with respect to coefficient a0 isshown in FIG. 19. White circle ◯ and solid black circle  in FIG. 19denote coefficients in each subband. The trees in upper area comprisecoefficients of the subbands having a lower resolution while the treesin lower area comprise coefficients of the subbands having a higherresolution.

In such a tree structure, the coefficients having lower resolution arereferred to as “parents” and the coefficients having next higherresolution in the same spacial position as designated by arrows arereferred to as “children”. In FIG. 19, for example, coefficient a0 is aparent for coefficients a1, a2 and a3, which are in turn children forcoefficient a0. Coefficient a1 is a parent for coefficients a10, a11,a12 and a13 and, coefficients a10, a11, a12 and a13 are children forcoefficient a1.

All coefficients having higher resolution in the same spacial positionwhich are linked with each other by arrows with respect to one parentare referred to as “descendants” and all coefficients having a lowerresolution in the same spacial position which are linked with each otherby arrows with respect to one child are referred to as “ancestors”. InFIG. 19, for example, the coefficients encircled with a dotted line aredescendants for coefficient al and coefficients a10, a1 and a0 areancestors for coefficient a100.

Then, the coefficients are quantized in the block basis. Three symbolsare assigned to each node of the trees for representing whether thequantization coefficient is zero or non-zero. Definition of the symbolwill now be described. The coefficient having the lowest frequency amongthe coefficients in which one coefficient in a tree is zero and thecoefficients of its descendants are all zero is referred to aszero-tree-root (ZTR). Since this coefficient and the coefficients havinga higher resolution than that of the former coefficient are all zero atthis time, it would be unnecessary to code the coefficients of itsdescendant if ZTR appear on a tree. When any one coefficient in a treeis not zero, but the coefficients of its descendant are all zero, thecoefficient in interest is referred to as valued zero-tree root (VZTR).If there is any one non-zero coefficient in the descendant, itscoefficient is referred to as “Value”.

White and solid black circles denote the coefficients which thequantizing value is zero and non-zero, respectively in FIG. 19. In thiscase, the coefficients which require coding are shown in FIG. 20. Sincea0 has a quantizing value which is not “zero” in FIG. 20, the symbolValue is assigned to code the quantizing value. Since a1 and itsdescendants (a10 through a13, a100 through a103 through a133) are allzero, symbol ZTR is assigned to a1 and it is not necessary to code thequantizing value. Since it can be found that the value of a1 is zero dueto the fact that a1 is ZTR, it is never necessary to code theinformation on the descendants of a1.

Since a2 has a quantizing value which is not zero, but its descendantsall have a quantizing value which is zero, symbol VZTR is assigned forcoding only the quantizing value of a2. Concerning the descendants ofa2, same as those of a1, it is not necessary to code their information.Since a3 has a quantizing value which is not zero and there are somedescendants which have a quantizing value which is not zero, symbolValue is assigned for coding the quantizing value. VZTR is assigned fora30. ZTR is assigned for a31. Value is assigned for a32 and a33. Onlythe quantizing values of the coefficients having the highest frequency(a320 through a333) are coded without assigning a symbol to thecoefficients. As mentioned above, the information to be coded on thisblock comprises:

symbol information including Value, ZTR, VZTR, Value, VZTR, ZTR, Value,Value, Value, Value, Value, . . . , Value and coefficient informationincluding Q(a0), Q(a2), Q(a3),

Q(a30), Q(a32), Q(a33), Q(a320), Q(a321), Q(a322), . . . , Q(a333),wherein Q(a) denotes the quantizing value of the coefficient a. Thecontents of coded data are shown in FIG. 21.

When the symbol is VZTR or Value, it is necessary to code the quantizingvalues of the coefficients. Since there are generally a lot ofcoefficients having a quantizing value which is zero in the highfrequency subband, many ZTRs are generated so that it is unnecessary tocode the coefficient value. Therefore high coding efficiency isachieved.

As mentioned above, in the ZTE technique the order of coding of thecoefficients does not shift subband by subband, but quantization of eachblock is conducted, then the symbol information and the coefficientinformation in the block basis is completely coded and thereafter codingof next block is initiated.

An image coding device using the ZTE technique is shown in FIG. 14 andan image decoding device using the ZTE technique is shown in FIG. 15. InFIG. 14, a reference numeral 1401 denotes a subband decomposing portionfor decomposing an image into subbands by means of a two-dimensionaldecomposing filter, 1402 denotes a block forming portion for forming ablock by collecting coefficients having a parent-child relationship fromthe decomposed subbands as shown in FIG. 18, 1403 denotes a quantizingportion for quantizing the coefficients in the block basis, 1404 denotesa symbol information determining portion for determining the symbolwhich is shown in FIG. 20 in the block basis from the coefficients afterthe quantization, 1405 denotes a symbol information coding portion forvariable-length coding each symbol information, 1406 denotes acoefficient coding portion for coding only the coefficients in which thesymbol information which is determined in portion 1404 corresponds toVZTR or Value, and 1407 denotes a data integrating portion forintegrating to array the symbol information before the coefficientinformation in one block. FIG. 22 is a flow chart showing a series ofthe operations.

In FIG. 15, a reference numeral 1501 denotes a data separating portionfor separating coded data into symbol information and coefficientinformation for each one block, 1502 denotes a symbol informationdecoding portion for variable-length decoding symbol information, 1503denotes a coefficient decoding portion for decoding the coefficientscorresponding to Value and VZTR based upon the decoded symbolinformation, 1504 denotes a block data reproducing portion forreproducing all coefficient values for one block based upon the decodedsymbol information and coefficient information, 1505 denotes an inversequantizing portion for inverse quantizing the quantized coefficients foreach block, 1506 denotes a subband image producing portion for producingthe whole subband image by relocating the coefficient values of allblocks to deblocking them, and 1507 denotes a subband synthesizingportion for performing a subband synthesis by means of a two-dimensionalsynthesizing filter. FIG. 23 is a flow chart showing a series ofoperations.

The subband coefficients can be efficiently coded and decoded in theblock basis by using the above-mentioned image coding and decodingdevices.

Since a block in which subband coefficients having a parent-childrelationship are collected is formed and coded in the ZTE technique insuch a manner, quantization in the block basis is possible. The codingefficiency can be improved by using a fact that most of the coefficientsof the high frequency are zero. On the contrary, the coded data can notbe provided with the scalability which the subband coding inherentlypossesses.

In other words, reproduced images having different resolutions can bedecoded from part of the coded data as shown in FIG. 24 in theconventional subband coding technique in which information on onesubband is coded and then the information on the subband having the nexthigher resolution is coded. If for example, the information on only LL3is decoded from the coded data, the whole image could be reproduced atthe lowest resolution.

If LL3, HL3, LH3 and HH3 among the coded data are decoded, the wholeimage can be reproduced at a resolution which is higher than the case ofdecoding of only LL3. If all coded data is decoded, the whole image canbe reproduced at the highest resolution.

However, in the ZTR technique, quantization in the block basis ispossible and the coding efficiency can be improved by using the factthat most of the coefficients of the high frequency subband is zero. Butif some of the coded data is decoded from the left and upper area of animage in the block basis, only part of the image can be reproducedalthough the regenerated part has a high resolution. In other words, thescalability which the subband inherently has is lost in the ZTEtechnique.

DISCLOSURE OF THE INVENTION

In order to overcome the above-mentioned problems,

(1) The present invention provides an image coding device comprisingmeans for decomposing an image into subbands to produce a first subbandimage; means for forming a blocked second subband image by collectingsubband coefficients having a parent-child relationship between subbandsin said first subband image to form a plurality of blocks; means forquantizing said subband coefficients of each block of said secondsubband image; means for determining symbol information representingwhether the quantized subband coefficient of said second subband imageis “0” or non “0”; means for relocating the symbol information of saidsecond subband image in accordance with the frequency position in saidfirst subband image; means for variable-length coding said relocatedsymbol information; means for relocating said quantized subbandcoefficients to be coded based upon said symbol information and forminga third subband image in accordance with the frequency position in saidfirst subband image; means for variable-length coding said relocatedsubband coefficients; and means for collecting and arranging said codedsymbol information and subband coefficients in each subband.

(2) The present invention comprises: means for separating said codeddata into symbol information and subband coefficients; means fordecoding said coded symbol information for each subband; means forreproducing said third subband image by decoding each of said subbandcoefficient based upon said decoded symbol information; means forforming said second blocked subband image comprising a plurality ofblocks which are formed by collecting said decoded subband coefficientshaving a parent-child relationship in each subband; means for inversequantizing said decoded subband coefficients of said second subbandimage; means for producing subband images which are relocated inaccordance with the frequency position in said third subband coefficientby deblocking said inverse quantized subband coefficients of said secondsubband image; and means for synthesizing said subband images to providea decoded image.

(3) There is provided means for arranging firstly all pieces of saidsymbol information in each subband and then arranging all said subbandcoefficients in each subband when said coded symbol information andsubband coefficients are collected into one group for each subband.

(4) There is provided means for conducting an operation for separatingthe coded data which is one group comprising the symbol information andsubband coefficients which are collected for each subband into allpieces of said symbol information in one subband firstly, and then intoall said subband coefficient information in one subband.

(5) There is provided means for arranging sets of said symbolinformation and said subband coefficient corresponding thereto inaccordance with the order of said symbol information in each subband,when said coded symbol information and subband coefficients arecollected into one group for each subband.

(6) There is provided means for conducting an operation for separatingthe coded data which is one group comprising the symbol information andsubband coefficients which are collected for each subband into saidsymbol information and said subband coefficient for each symbol for allsubbands in said coded data.

(7) In lieu of said symbol information coding portion, said coefficientinformation coding portion and said coded data integrating portion,there are provided means for forming a set of the symbol information andsubband coefficient corresponding to said symbol information, and meansfor variable-length coding said set of said symbol information andsubband coefficient information.

(8) In lieu of said decoded data separating portion, said symbolinformation decoding portion and said coefficient information decodingportion, there are provided means for decoding a set of said symbolinformation and subband coefficient information and means for separatingsaid decoded set into symbol information and coefficient information.

(9) There is provided means for inserting “0” into the subbandcoefficient value which can not be decoded if complete coded data whichis produced by said image coding device can not be inputted.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a block diagram showing an embodiment of the invention.

FIG. 2 is a block diagram showing an embodiment of the invention.

FIG. 3 is a diagram explaining the present invention.

FIG. 4 is a diagram explaining the present invention.

FIG. 5 is a diagram explaining the present invention.

FIG. 6 is a flow chart explaining the operation of the presentinvention.

FIG. 7 is a flow chart explaining the operation of the presentinvention.

FIG. 8 is a block diagram showing an embodiment of the presentinvention.

FIG. 9 is a flow chart explaining the operation of the presentinvention.

FIG. 10 is a block diagram showing an embodiment of the presentinvention.

FIG. 11 is a block diagram showing an embodiment of the presentinvention.

FIG. 12 is a flow chart explaining the operation of the presentinvention.

FIG. 13 is a flow chart explaining the operation of the presentinvention.

FIG. 14 is a block diagram showing the prior art.

FIG. 15 is a block diagram showing the prior art.

FIG. 16 is a diagram explaining the prior art.

FIG. 17 is a diagram explaining the prior art.

FIG. 18 is a diagram explaining the prior art.

FIG. 19 is a diagram explaining the prior art.

FIG. 20 is a diagram explaining the prior-art.

FIG. 21 is a diagram explaining the prior art.

FIG. 22 is a f low chart explaining the operation of the prior art.

FIG. 23 is a flow chart explaining the operation of the prior art.

FIG. 24 is a diagram showing the scalability of the subbanddecomposition.

FIG. 25 is a diagram explaining the problems of the prior art.

BEST MODES FOR EMBODYING THE PRESENT INVENTION

Now, embodiments of an image coding device and image decoding device ofthe present invention will be described in detail with reference to thedrawings.

FIG. 1 is a block diagram showing a first embodiment of the codingdevice of the present invention. In the drawing, a reference numeral 101denotes a subband decomposing portion, 102 denotes a block formingportion, 103 denotes a quantizing portion, 104 denotes a symbolinformation determining portion, 105 denotes a symbol information codingportion, 106 denotes a coefficient coding portion. These portions 101,102, 103, 104, 105 and 106 are identical in structure with those 1401,1402, 1403, 1404, 1405 and 1406, respectively, which are shown in FIG.14.

In other words, by means of the subband decomposing portion 101, blockforming portion 102, quantizing portion 103 and the symbol determiningportion 104, an image is decomposed into subbands, which are dividedinto blocks as shown in FIG. 18. Then, the subband coefficients arequantized for each block. This operation is similar to that of the priorart. Quantization is conducted in the block basis although all blocksmay be quantized in the same quantization stepsize in a special case. Inthe present embodiment, the symbols and the quantization coefficients inFIG. 18 which are produced by the prior art are divided and relocated ineach subband so that subband images are produced again. And coding ofthe symbol information and coefficient information is conducted in orderfrom the subband having a lower resolution.

A reference numeral 108 in FIG. 1 denotes the symbol informationrelocating portion which relocates the symbol information which isprepared for each block by the prior art for each subband. One block ofthe blocked subband image which is produced by the prior art in FIG. 18corresponds to the block in a part (a) of FIG. 3. The portion 108 inFIG. 1 conducts the relocation of the symbol from the part (a) to a part(b) of FIG. 3 for each block for producing a new subband image to outputit to the memory 110.

Since no symbol exists with respect to the coefficients of thedescendants of ZTR and VZTR, a symbol “SKIP” is written into the memory110 and the symbol information of SKIP is not coded when coding isconducted. The hatched areas denote SKIP in FIG. 3. As mentioned in thedescription of the prior art, where there is no symbol information inthe subband having a highest frequency in the part (b) of FIG. 3.

A reference numeral 109 in FIG. 1 denotes a coefficient relocatingportion which relocates the coefficient information which is quantizedfor each block by the prior art for each subband. One block of theblocked subband image which is produced by the prior art in FIG. 18corresponds to the block in the part (a) of FIG. 3. The portion 109 inFIG. 1 conducts the relocation of the coefficient information from thepart (a) to a part (c) of FIG. 3 for each block for producing a newsubband image to output it to the memory 111. However, in relation withthe coefficients corresponding to SKIP stored in the memory 110, thesymbol of the SKIP is written in lieu of the coefficient value asmentioned above and is not coded when coding is conducted.

Relocation of the symbols from the part (a) to (b) of FIG. 3 and therelocation of the coefficient values from the part (a) to (c) of FIG. 3may be conducted by overwriting the relocated symbols and coefficientvalues into a memory in which the symbols and coefficient values arecollected for each block which is shown in FIG. 18 without using thememories 110 and 111 in FIG. 1 and by conducting the subsequentprocessing by the operation of addresses corresponding to thepredetermined positions in memories 110 and 111.

For simplicity of the description, the present embodiment will bedescribed with reference to only the case in which the symbols andcoefficient values are written into the memories 110 and 111. Similarprocessing can be conducted by performing an address calculation in FIG.18 to reach the block corresponding to the above-mentioned memories 110and 111.

A reference numeral 107 in FIG. 1 denotes the coded data integratingportion for collectively arranging the symbol information andcoefficient information for each subband, which is stored in thememories 110 and 111. The method of integrating the symbol informationand coefficient information includes two methods which are shown in apart (a) and (b) of FIG. 4. The part (a) of FIG. 4 shows an example ofcontents of the coded data when the symbol information and thecoefficient information is collectively arranged for each subband.

In the coded data integrating portion, the symbol information andcoefficient information is consecutively input starting from that in thesubband having the lowest frequency to the subband having higherfrequency. After the symbol information of one subband is written intothe coded data, the coefficient information of one subband is writteninto the coded data. Then the symbol information of one subband having afrequency which is higher by one level is written into the coded data.Such an operation is repeated until the subband having the highestfrequency. The part (b) of FIG. 4 shows another example of the contentsof the coded data when the symbol information and coefficientinformation is collectively arranged for each subband.

In the coded data integrating portion, firstly one set of the symbolinformation corresponding to one coefficient and one-coefficientinformation corresponding to this symbol information is written into thecoded data and then similarly one set of symbol information of onecoefficient and the coding information corresponding thereto is writteninto the coded data. This operation is repeated until the subband havingthe highest frequency. Since there is no coefficient information for thecoefficients corresponding to ZTR and SKIP at this time, there is noinput so that symbol information is successively input. Since no symbolinformation exists for the subbands having the highest frequency (HL1,LH1, HH1) as mentioned in the description of the prior art, only thecoefficient information is coded. The coded data of the symbolinformation and coefficient information in the part (b) of FIG. 4 willbe shown. S denotes symbol information and C denotes coefficientinformation.

A part (a) of FIG. 6 is a flow chart showing one example of operation ofthe image coding device in FIG. 1. A part (b) of FIG. 6 is a flow chartfor preparing coded data in the part (a) of FIG. 4. A part (c) of FIG. 6is a flow chart for preparing coded data in the part (b) of FIG. 4.

As mentioned above, scalability can be provided to the coded data byproducing the coded data in order starting from the subband having lowerresolution to the subband having higher solution by the relocation ofthe symbol information and coefficient information in the coding devicein the first embodiment of the present invention.

Now, the decoding device will be described.

FIG. 2 shows a first embodiment of the decoding device of the presentinvention for decoding the coded data which is prepared by the codingdevice of the first embodiment of the present invention. Prior to theinverse quantization in the prior art which the coded data is decodedfor reproducing the blocked subband images, which are inverse quantizedfor each block, deblocked them to produce subband images, synthesized toprovide a reproduced image, the symbol information and coefficientinformation is separated and decoded from the coded data and the decodeddata is relocated for each subband for producing the whole of subbandimage and then an additional processing of blocking for inversequantization is conducted.

A reference numeral 201 in FIG. 2 denotes a coded data separatingportion for separating the coded data into the symbol information andcoefficient information to output the resultant information into thesymbol information decoding portion 202 and the coefficient decodingportion 203. When the coded data of, for example the part (a) of FIG. 4is input, a boundary between the coded symbol information of one subbandand the coded coefficient information of one subband corresponding tothe symbol information is detected and the symbol and coefficientinformation is output to the symbol information decoding portion andcoefficient decoding portions, respectively.

Such an operation is repeated for all subbands. When the coded data of,for example the part (b) of FIG. 4 is input, a boundary between thecoded one symbol information and the coded coefficient informationcorresponding to the symbol information is detected and the symbol andcoefficient information is output to the symbol information decodingportion and coefficient decoding portions, respectively. Such anoperation is repeated for all subbands. However, the symbol informationis consecutively input since there is no relevant coefficientinformation when the symbol is ZTR. A reference numeral 208 denotes amemory for storing therein the symbol information which has beenvariable-length decoded by the symbol information decoding portion 202to position corresponding to that on the subband images as shown in thepart (b) of FIG. 3.

Since no symbol having a parent-child relationship, which is higher inresolution exists when the symbol of a tree is ZTR or VZTR, SKIP iswritten in the memory 208 and no symbol is overwritten thereon similarlyto the coding device. A reference numeral 209 denotes a memory forstoring therein the coefficient information which has beenvariable-length decoded by the coefficient decoding portion 203 toposition corresponding to that on the subband images as shown in thepart (c) of FIG. 3. Since no coefficient having a parent-childrelationship, which is higher in resolution exists when the symbol ofthe corresponding tree is ZTR or SKIP, “0” is written in the memory 209and no coefficient value is overwritten thereon similarly to the codingdevice.

However, the operation in the decoding device is different from that inthe coding device only in that “0” is written in the memory in lieu of“SKIP” in the coding device. The coefficient having a parent-childrelationship between the subbands are collected by the block formingportion 204 and based upon the coefficients stored in the memory 209 forforming blocks which are shown in the part (a) of FIG. 3. Thereafter, asmentioned in the description of the prior art, the quantizedcoefficients are inverse quantized for each block by the inversequantizing portion 205 and the coefficient values of all blocks arerelocated by the subband image producing portion 206 for deblocking toproduce the whole of the subband images. A reproduced image can beobtained by synthesizing the subbands by the subband synthesizingportion 207 using a two dimensional synthesizing filter.

The symbol information decoding portion 202, coefficient decodingportion 203, inverse quantizing portion 205, subband image producingportion 206, subband synthesizing portion 207 and the block formingportion 204 are identical in structure with the portions 1502, 1503,1505, 1506, 1507 which are shown in FIG. 15 and the portion 104 shown inFIG. 1, respectively. A flow chart showing a series of operations isshown in FIG. 7.

As mentioned above, the coded data having scalability can be decoded inthe decoding device of the first embodiment of the present invention.

FIG. 10 shows another example in which the coding device of the firstembodiment of the present invention is implemented. The differencebetween the devices which are shown in FIGS. 10 and 1 resides in that aset forming portion 1005 and a set coding portion 1006 are incorporatedin lieu of the symbol information coding portion 105, coefficient codingportion 106 and coded data integrating portion 107. Although the symbolinformation and the coefficient information is independentlyvariable-length coded and arranged in the above-mentioned coding deviceof the first embodiment, the symbol information and coefficientinformation is variable-length coded after the set of the symbol andcoefficient information in the present example has been formed.

A set of one item of symbol information and coefficient informationcorresponding to this symbol information is prepared by the set formingportion 1005. Since no symbol information exist in the subbands havingthe highest frequency (HL1, LH1, HH1), the coefficient information istreated one item by one item. If only symbol information exists in thesubbands having a frequency excepting the highest frequency and nocorresponding coefficient information exists (ZTR), only symbolinformation is treated. Now, an example of sets of symbol informationand coefficient information is shown. S denotes the symbol information,C denotes coefficient information, parentheses denote sets.

The set coding portion 1006 is adapted to variable-length codes the setsof symbol information and coefficient information which are formed bythe set forming portion 1005. The specific variable-length coding methodmay include two-dimensional Huffman coding of the symbol information andthe coefficient information, variable-length coding in which the samesymbols are consecutive if only symbol information is consecutive andone-dimensional Huffman coding if only coefficients are consecutive. Aflow chart of a series of operations is shown in FIG. 12.

As mentioned above, the symbol information and coefficient informationare relocated in another coding device of the first embodiment of thepresent invention. Accordingly, it can be formed the coded data to havethe scalability by forming from lower resolution subbands to higherresolution subbands in order.

FIG. 11 shows another example in which the decoding device of the firstembodiment of the present invention is implemented.

The differences between the devices which are shown in FIGS. 11 and 2reside in that a set decoding portion 1101 and a set separating portion1102 are incorporated in lieu of the coded data separating portion 201,the symbol information decoding portion 202, and coefficient decodingportion 203. Although the symbol information and the coefficientinformation which has been independently coded is variable-length codedafter the separation thereof in the decoding device of theabove-mentioned embodiment, the set of the symbol information andcoefficient information is variable-length coded and thereafter isseparated into the symbol information and coefficient information in thepresent case.

In the set decoding portion 1101, coded data in which the set of thesymbol information and the coefficient information which isvariable-length coded by the coding device shown in FIG. 10 isvariable-length decoded. Since no symbol information exists in thesubbands having the highest frequency (HL1, LH1, HH1) similarly to thedescription of the coding in this case, only the coefficient informationis decoded. The set of the symbol information and the coefficientinformation which has been decoded in the set decoding portion 1101 isseparated into the symbol information and coefficient information by theset separating portion 1102 so that it is output to the memories 1108and 1109. A flow chart showing a series of these operations is shown inFIG. 13.

As mentioned above, coded data having scalability can be decoded byanother decoding device of the first embodiment of the presentinvention.

FIG. 8 shows a second embodiment of the decoding device of the presentinvention. Coding device is identical with that of the first embodiment.

The differences between the devices shown in FIGS. 8 and 2 reside inthat a data interpolating portion 810 is added in the device shown inFIG. 8. If the coded data which has been prepared by image coding deviceis not completely input to the image decoding device or if all the codeddata which has been transmitted can not decoded due to low processingspeed of the image decoding device, the last half of the coded data maynot be input to the image decoding device.

FIG. 5 shows the contents of the memories 808 and 809 in FIG. 8 when theleading portion of the coded data having scalability which is input tothe image decoding device. Since the coded data which has been preparedby the image coding device of the first embodiment has the hierarchicalstructure from the information of the subbands having lower frequency tothe information of the subbands having higher frequency, the symbolinformation and the coefficient information which has been decoded fromthe discontinued coded data exists as represented by hatched area in apart (a) of FIG. 5.

In the part (a) of FIG. 5, blanks denote the coefficients in which theinformation on the coded data does not exist so that the information cannot be decoded. The data interpolating portion 810 in FIG. 8 substitutesthe coefficients of the blanks in the part (a) of FIG. 5 for “0” tointerpolate all coefficients of the subband image. Since data on onlypart of the HL2 in the second hierarchical level of the subband existsin this case, the reproduced image area corresponding to this part has ahigher resolution in a horizontal direction.

Since all the coefficients of the subband images are collected by thedata interpolating portion 810, blocking can be achieved as shown in apart (b) of FIG. 5 by the block forming portion 804 in FIG. 8.Alternatively, interpolation can be conducted for the coefficientinformation by the data interpolating portion 810 after the stage of thecoefficient decoding portion 803.

The part (a) of FIG. 5 shows a case the coded data is discontinued inthe course of the subband HL2. In the part (b) of FIG. 5, half-tonedupper half area is an area having a relatively higher resolution inwhich coded data up to LL3, HL3, LH3, HH3 and HL2 exists in each blockwhen blocking is conducted while lower half area is an area having arelatively lower resolution in which coded data up to LL3, HL3, LH3 andHH3 exists in each block when blocking is conducted.

The subsequent operation can be proceeded as is similarly to thedecoding device of the above-mentioned first embodiment. A reproducedimage when only part of the coded data is decoded in such a manner isshown in a part (c) of FIG. 5. The part (c) of FIG. 5 is relevant to thepart (a) of FIG. 5. Images having higher resolution can be obtained inupper half of the screen while images having a resolution which is onelevel lower in a vertical direction than that of upper half screen isobtained in the lower half of the screen. A flow chart showing a seriesof the operations is shown in FIG. 9.

As mentioned above, the whole of the image can be decoded from part ofthe coded data having scalability by the decoding device of the secondembodiment of the present invention. Coded data having a desiredquantity of data can be reproduced substantially consecutively from theleading portion of the coded data when only part of the coded data isdecoded. In other words, an image can be reproduce even if decoding isterminated in a desired position of the coded data.

As mentioned above, the reproduced image of the whole image can beobtained from part of the coded data by providing the coded data withscalability in accordance with the present invention.

INDUSTRIAL UTILITY

(1) The image coding device of the present invention is capable ofimplementing of the scalability of the coded data, which has beenimpossible, while conducting conventional quantization in the blockbasis by the relocation of the information in the subband basis forpreparing coded data after conducting subband decomposition of the imageand performing coding process in the block basis.

(2) Since the image coding device of the present invention can achievequantization in the block basis to control of bit assignment for eachblock so that high quality of image can be achieved.

(3) Since the coded data has scalability in accordance with the presentinvention, the whole of the image can be reproduced from part of thecoded data having scalability in the image decoding device.

(4) Since the coded data has scalability in accordance with the presentinvent ion, the quantity of data to be decoded can be specified to adesired number of bits in the image decoding device when only part ofthe coded data is decoded.

What is claimed is:
 1. An image coding device comprising: a subbanddecomposing portion for decomposing an image into subbands to produce afirst subband image; a block forming portion for forming a blockedsecond subband image by collecting subband coefficients having aparent-child relationship between subbands in said first subband imageto form a plurality of blocks; a quantizing portion for quantizing saidsubband coefficients of each block of said second subband image; asymbol information determining portion for determining symbolinformation representing whether the quantized subband coefficient ofsaid second subband image is “0” or non “0”; a symbol informationrelocating portion for relocating the symbol information of said secondsubband image in accordance with a frequency position in said firstsubband image; a symbol information coding portion for performingvariable-length coding of relocated symbol information and generatingcoded symbol information; a coefficient relocating portion forrelocating said quantized subband coefficients to be coded based uponsaid symbol information and forming a third subband image in accordancewith the frequency position in said first subband image; a coefficientcoding portion for performing variable-length coding of said relocatedquantized subband coefficients and generating coded quantized subbandcoefficients; and a coded data integrating portion for collecting andarranging said coded symbol information and said coded quantized subbandcoefficients in order of resolution level, whereby the coded data isprovided with a hierarchical structure.
 2. An image coding device asdefined in claim 1, wherein said coded data integrating portion collectsand arranges symbol information and subband co-efficients with symbolinformation being arranged before subband coefficients, and with thesubbands being arranged from relatively lower resolution to relativelyhigher resolution.
 3. An image coding device as defined in claim 1,wherein said coded data integrating portion forms sets of a symbolinformation and a subband coefficient corresponding thereto for subbandswhich are arranged from relatively lower resolution to relatively higherresolution.
 4. An image decoding device for decoding coded data having ahierarchical structure comprising: a coded data separating portion forseparating inputted coded data into symbol information and subbandcoefficients, said inputted coded data having symbol informationrepresenting whether a corresponding quantized subband coefficient is“0” or non “0” and a subband coefficient, wherein symbol information andsubband coefficients are arranged in order of resolution level; a symbolinformation decoding portion for decoding separated symbol information;a coefficient decoding portion for reproducing a third subband image bydecoding each of said subband coefficient based upon said decoded symbolinformation; a block forming portion for forming a blocked secondsubband image comprising a plurality of blocks which are formed bycollecting said decoded subband coefficients having a parent-childrelationship between subbands; an inverse quantizing portion forinversely quantizing said decoded subband coefficients of said secondsubband image; a subband image producing portion for producing firstsubband images which are relocated in accordance with the frequencyposition in a third subband coefficient by deblocking said inversequantized subband coefficients of said second subband image; and asubband synthesizing portion for synthesizing said subband images toprovide a decoded image.
 5. An image decoding device as defined in claim4, wherein said coded data separating portion separates the coded datainto collected symbol information and then into subband coefficients forsubbands wherein the subbands in the coded data are arranged fromrelatively lower resolution to relatively higher resolution.
 6. An imagedecoding device as defined in claim 4, wherein said coded dataseparating portion separates the coded data into a symbol informationfor each symbol and a subband coefficient corresponding to the symbolinformation, and the coded data includes subbands arranged fromrelatively lower resolution to relatively higher resolution.
 7. An imagedecoding device as defined in claim 4, further comprising: a datainterpolating portion for inserting “0” into a value of subbandcoefficient which can not be decoded if only part of coded data which isproduced by said image coding device is inputted, whereby a reproducedimage is obtained by decoding only part of coded data having ahierarchical structure.
 8. An image coding device comprising: a subbanddecomposing portion for decomposing an image into subbands to produce afirst subband image; a block forming portion for forming a blockedsecond subband image by collecting subband coefficients having aparent-child relationship between subbands in said first subband imageto form a plurality of blocks; a quantizing portion for quantizing saidsubband coefficients in each block of said second subband image; asymbol information determining portion for determining symbolinformation representing whether the quantized subband coefficient ofsaid second subband image is “0” or non “0”; a symbol informationrelocating portion for relocating the symbol information of said secondsubband image in accordance with the frequency position in said firstsubband image; a coefficient relocating portion for relocating saidquantized subband coefficients to be coded based upon said symbolinformation and forming a third subband image in accordance with thefrequency position in said first subband image; a set forming portionfor forming a set of said symbol information and subband coefficientcorresponding to said symbol information, with a plurality of sets beingarranged in order of resolution level; and a set coding portion forperforming variable-length coding of said set of said symbol informationand subband coefficient, whereby the coded data is provided with ahierarchical structure.
 9. An image decoding device for decoding codeddata having a hierarchical structure, comprising: a set decoding portionfor decoding a set of a symbol information and subband coefficient ininputted coded data having a set of a symbol information representingwhether a quantized subband coefficient is “0” or non “0” and a subbandcoefficient, where a plurality of sets are arranged in order ofresolution level; a set separating portion for separating said decodedset into symbol information and subband coefficient to reproduce a thirdsubband image; a block forming portion for forming a second blockedsubband image including a plurality of blocks which are formed bycollecting said decoded subband coefficients having a parent-childrelationship between subbands; an inverse quantizing portion forinversely quantizing said decoded subband coefficients of said secondsubband image; a subband image producing portion for producing firstsubband images which are relocated in accordance with a frequencyposition in a third subband coefficient by deblocking said inversequantized subband coefficients of said second subband image; and asubband synthesizing portion for synthesizing said subband images toprovide a decoded image.